8 PATAGONIAN EXPEDITIONS PALEONTOLOGY. 



It seems probable that Steinmann's clay-shale system includes the 

 Pueyrrydon series, but of the few fossils that he cites not one is repre- 

 sented in Mr. Hatcher's collection by similar species, nor even by the 

 same genus, unless it is the ammonite, which is not cited with sufficient 

 definiteness to permit comparisons. 



The collections studied by Behrendsen came from a region 500 to 800 

 miles north of Lake Pueyrrydon. From them he determined the pres- 

 ence of several Jurassic and Cretaceous horizons, including Lias, Lower 

 Oolite, Tithonian, Neocomian, Aptian (Gault), and Upper Cretaceous. 

 The small number of species cited from some of the localities and horizons, 

 however, must have made part of these determinations doubtful. 



At one locality on the Arroyo Pequenco, between Rio Salado and Rio 

 Malargue, strata referred to the Upper Neocomian yielded only Exogyra 

 con/oni, fragmentary remains of a Crustacean, a poorly preserved Trigonia 

 that is compared with T. aliformis, a Rhynchonella, and Mytilus cumeri. 

 The fact that some of the European forms referred to E. couloni differ 

 so much from the typical form that they may be compared with Ostrea 

 tardensis, suggested that the latter may be the form referred to E. couloni 

 by Behrendsen, but his description and the figures to which he especially 

 refers for comparison indicate a very different form. A poorly preserved 

 specimen of Trigonia subventricosa might also reasonably be compared 

 with T. aliformis. There is a possibility therefore that the Pequenco 

 horizon may be the same as a part of the Pueyrrydon series. 



The Aptian or Gault of Behrendsen's paper is represented by a few 

 fossils from " Portezuelo de Carqueque," some distance north of the last 

 mentioned locality. The only forms listed from this horizon are Am- 

 monites sp., Ostrea sp., Pecten sp., and Serpula phillipsi Roemer, the last 

 named species evidently being the basis of the determination of the age 

 of the bed. The Ostrea is a mere unidentifiable fragment and the de- 

 scriptive notes on the Ammonites and the Pecten make it certain that they 

 can not be identical with any of the Pueyrrydon species. Serpula pJril- 

 lipsi, however, as described and figured from the Gault of England and 

 Germany has considerable resemblance to the form I have described as 

 Tnbnlostinm pitpoides, though for reasons pointed out in the description 

 of the latter species it is not considered identical nor even congeneric. 

 It is mentioned here merely as an example of possible identity that may 

 some time be established by comparison of specimens from the two re- 



